In Japanese Patent Application, First Publication No. H11-153386, a mist cooling apparatus is disclosed that is used in heat treatment on a treatment object such as a metallic material, and cools the treatment object. The mist cooling apparatus sprays mist-like cooling liquid onto the heated treatment object and performs cooling by using the latent heat of vaporization of the cooling liquid. For this reason, the cooling ability of the mist cooling apparatus is higher than a gas spray type cooling apparatus in the related art. Further, by adjusting the amount of sprayed mist, it is possible to easily perform control of the cooling rate of the treatment object, which has been difficult in an immersion type cooling apparatus in the related art.